My present invention relates to a so-called can for a centrifugal pump motor and, more particularly, to a cup-shaped member which is located between the rotor and stator of an electric motor, especially a motor driving a centrifugal pump and particularly a motor driving a centrifugal pump for the circulation of water in a heating or cooling system and which separates a wet side from a dry side of the pump and motor. The invention is directed, therefore, to a cup which serves in a canned motor-pump assembly to confine a liquid which may serve to cool the electric motor and which communicates with the pump portion of the assembly for that purpose. More particularly this invention concerns a xe2x80x9ccanxe2x80x9d or xe2x80x9ccupxe2x80x9d which the usually, but not necessarily, is composed of a synthetic resin material, can receive at least one and preferably both bearings journaling the motor shaft, surrounds the rotor of the motor, and separates the rotor space from the stator space which surrounds the cup. The invention also relates to a device for and a method of making the cup by injection-molding of a synthetic resin.
So-called motor-pump systems are generally known. With such pumps, operating in accordance with the wet-running principle, a cup separates the wet space from the dry space in the motor driving the pump. The cup has usually been composed of metal, hence the term xe2x80x9ccan,xe2x80x9d although it can be made of synthetic resin. The cup serves to receive the entire rotor assembly in most cases comprising the rotor, its shaft, and ball, roller or plain (slide) bearings.
Reference may be had, for example, to the commonly-owned copending application Ser. No. 09/202,696 filed Dec. 17, 1998, (now U.S. Pat. No. 6,091,174) and the following commonly-assigned copending applications: Ser. No. 09/320,906 filed May 27, 1999 and Ser. No. 09/410,002 filed Sep. 30, 1999 (now U.S. Pat. No. 6,229,240).
The fabrication of the cup from synthetic resin has the advantage that it can be of lighter weight and can be fabricated less expensively and, because of the lighter weight, the motor efficiency can be greater.
When the cup is fabricated from metal, a seat for a bearing is provided at a bottom of the cup in the form of a metal sleeve or by imparting a bearing-receiving shape to the cup so that it is integrated in the cup. A radial bearing is generally press-fitted in the bearing seat and has an outer shape which corresponds to that of the metal sleeve or the configuration of the seat imparted directly to the cup so that a force-fit between the bearing outer race and the seat is ensured.
When the cup is formed from synthetic resin, however, a variety of problems can arise. For example, the synthetic resin material may relax in operation to relieve a press-fit between the bearing and the seat. As high temperatures arise in the motor/pump assembly, the press-fit can be lost because of the difference in the thermal coefficients of expansion of the bearing and the cup.
Even when the assembly is used at low temperatures, drawbacks are encountered in the use of a synthetic resin cup to separate the rotor assembly from the stator space. The different coefficients of thermal expansion of the bearing and cup give rise to increased forces between the cup and the bearing in the pressing zone which can lead to rupture of the bearing seat.
It is, therefore, the principal object of the present invention to provide an improved structurally simple low-cost and easily-handled cup for the purposes described that can operate reliably for long periods of time without the danger of separation of the bearing from its seat.
Another object of this invention is to provide an improved cup for a so-called canned motor/pump (circulating or centrifugal pump) assembly whereby drawbacks of earlier cups composed of synthetic resin are obviated.
It is also an object of this invention to provide a method of simply and economically fabricating the improved cup.
It is also an object of this invention to provide a device for carrying out that method, i.e. for producing an economically, reliable and long-lived cup for enclosing the rotor assembly of an electric motor.
These objects and others which will become apparent hereinafter are attained, in accordance with the invention, in a cup for a canned circulating pump or synthetic pump, i.e. for a motor/pump assembly, which is at least predominantly composed of synthetic resin and wherein at least one bearing journaling the motor shaft is disposed wherein at least the bottom of the cup is formed with a bearing seat in which a bearing axially, radially and torsionally form-fittingly is retained in the cup. The term xe2x80x9ctorsionally retainedxe2x80x9d is intended to mean that the outer race of the bearing is held in the cup form-fittingly without rotation therein.
It is important, therefore, that at least at the bottom of the cup a bearing be held form-fittingly therein in the axial sense, in the radial sense and torsionally. The form-fitting connection in the axial sense means that the bearing cannot shift in the axial direction while the radial retention means that there is no significant radial play between the bearing and the synthetic resin cup either. Although the bearing is not press-fitted into the seat, it forms a transition fit or low-play fit therewith.
This permits the cup to be of a relatively simple construction from a synthetic resin material but which is capable of retaining the bearing and the cup even with highly fluctuating temperatures in a reliable manner with a transition or slight-play fit between the bearing and the synthetic resin cup. The different coefficients of thermal expansion between the bearing and the cup do not give rise to the aforedescribed problems. The handling, for example, of the assembly, is simple and the cup can be fabricated in an economical manner.
It has been found to be especially advantageous to form the radial bearing which is remote from the pump so that it can be snapped form-fittingly into the bottom of the cup. In this way, the mounting of the bearing is both rapid and simple.
The snap connection can be formed in an especially simple manner by providing at least one retaining arm which is elastically biased outwardly in a radial direction and extends axially in a direction toward the pump and has a radially-inwardly extending projection or finger for engagement behind the radial bearing as it is snapped into its seat. Preferably four such detent arms are provided in an angularly-equispaced relationship around the axis of the radial bearing and for their projections extending inwardly and diametrically opposite each other in pairs.
The detent arms can be easily pressed outwardly during mounting of the bearing when the projections, on their sides turned toward the pump are beveled to form a ramp which presses the arms outwardly. The end of the bearing turned away from the pump can be beveled similarly for this purpose. A defined axial positioning of the bearing can be obtained when, at the bottom of the cup a shoulder or pedestal is provided which lies against the face of the bearing turned away from the pump. A defined radial positioning of the bearing is ensured by forming the body of the cup with axially-extending rigid centering elements for the radial centering of the radial bearing. A rotation of the bearing or of the outer race can be prevented in a simple manner by having the projections of the detent arms form-fittingly engaged in respective recesses of the radial bearing.
It is advantageous to form the detent arms and/or the centering elements in one piece with the remainder of the cup by injection-molding or casting them as part of the bottom of the cup. This eliminates the need for additional mounting space to provide such elements on the cup. A device for making the cup of the invention by injection-molding comprises a pair of mutually coaxial cores located one inside another and axially shiftable relative to one another into a removal position and angularly-disposable relative to one another in the removable position.
With such cores and an outer mold member, the injection-molding form can be provided to simply inject the cup with the undercuts on the projections. The cores should, for this purpose, be movable relative to one another axially with a displacement which is equal to the length of the detent arm or centering element.
It is especially advantageous when the outer core defines the radial lateral flanks, the free end faces and the radial outwardly surfaces of the detent arms and centering elements while the inner core defines the radially-inwardly surfaces of the indexing arms and centering elements as well as the undersides of the projections, i.e. the undercuts. With such a molding die the cup can be produced economically and simply by injection molding and for removal of the cup. Initially the outer core is retracted by at least the length of the detent arms or centering elements to provide a free space for the detent arms to be deflected outwardly. Then the inner core is rotated through an angle corresponding to the peripheral width of the projection to bring the ledge of the inner core which formerly was positioned beneath each projection into spaces between projections or adjacent the detent arms. Then the inner form or core is retracted axially. The cup can then be removed from the outer mold body defining its external shape.